Southern Hemisphere midlatitude atmospheric variability of the NCEP‐NCAR and ECMWF reanalyses

We compare the representation of the Southern Hemisphere midlatitude winter variability in the NCEP‐NCAR and ERA40 reanalyses by using the Hayashi spectral technique. We find important discrepancies in the description of the atmospheric waves at different spatial and temporal scales. ERA40 is generally characterized by a larger variance, especially in the high‐frequency spectral region. Compared to the Northern Hemisphere, the assimilated data are relatively scarce particularly over the oceans, and they provide a weak constraint to the assimilation system even in the period when satellite data are available. In the presatellite period the discrepancies between the two reanalyses are large and randomly distributed; after 1979 the discrepancies are systematic. This study suggests that, as for the winter midlatitude variability in the Southern Hemisphere, a well‐defined picture to be used in the evaluation of climate model simulations is still lacking because of the nonconsistency of the reanalyses.